The invention relates to an objective lens holding apparatus and particularly to an objective lens holding apparatus adopted for use on optical pick-up heads of optical reading devices (such as CD-ROM, DVD-ROM and the like) to ensure that the objective lenses move stability in the tracking and focusing direction to accomplish tracking and focusing servo operations.
Using laser beams (such as semiconductor lasers) to pick up records on optical media (such as CDs or DVDs) is a technique known in the art. The laser beam is focused on the track located on the surface of the optical disk by means of an objective lens in the optical pick-up head. A photo detector converts the return light reflected from the optical disk into regenerated signals to obtain the data recorded on the optical disk. During data pick-up processes, tracking signals and focusing signals must be obtained from the return lights, and based on these signals the tracking actuator and the focusing actuator may be controlled to move the objective lens and ensure that the laser beam focuses correctly on the desired track on the surface of the optical disk.
In order to accomplish the servo operations of tracking and focusing, the objective lens must be able to move freely in the optical axis direction (i.e. the focusing direction) and the radial direction of the optical disk (i.e. the tracking direction). Hence a special holding apparatus for supporting the objective lens is required to provide stability movement. The known holding apparatus for supporting the objective lens can be classified as follows:
1. Wire-supporting type: U.S. Pat. Nos. 5,381,273, 5,555,623 and 5,587,845 disclose this type of technique in which the objective lens is supported by four elastic metallic wires (such as stainless steel wires). The metallic wires are parallel to one another. One end of the wires is fixed while the other end of the wires connects to a lens holder. The objective lens holder and the objective lens may be moved in two different directions under the driving of a tracking actuator and a focusing actuator to accomplish the servo operations. However, such a design tends to produce twisting on the metallic wires during the servo operations of tracking and focusing. As a result, tracking and focusing operations are prone to error.
2. Objective lens holder employing leaf spring: U.S. Pat. No. 5,892,628 discloses such a technique. It utilizes four parallel leaf springs to support the objective lens. U.S. Pat. No. 5,453,881 also discloses a technique that uses two parallel springs, an upper leaf spring and lower leaf spring, to support the objective lens. Both of these techniques are difficult to produce and assemble.
3. Axial sliding and rotating type device: U.S. Pat. No. 5,587,845 discloses such a technique. In the FIG. 1 of this patent, the objective lens holding device includes a supporting shaft for holding an objective lens holder and an objective lens. The objective lens holder and the objective lens may slide axially along the supporting shaft under the driving of the tracking actuator and the focusing actuator, or swing about the axis of the supporting shaft to accomplish the servo operations of tracking and focusing. However such a design requires precise matching dimensions for the objective lens holder and the supporting shaft. Thus it increases manufacturing difficulty. Furthermore, in the event that the supporting shaft and objective lens holder do not match properly, the objective lens holder tends to wobble.
In addition, employing the objective lens holders set forth above, the objective lens incurs variations of an inclined angle on the tangent line of the track while the pick-up head reads the optical disk. As a result, reading effectiveness is adversely impacted. Therefore, there is a need to develop an improved objective lens holder to remedy the disadvantage of variation of the inclined angle and to increase reading effectiveness.
The primary object of the invention is to provide an objective lens holding apparatus to prevent the objective lens from incurring an inclined angle during yawing when the optical pick-up head reads/writes the optical disk, and to keep the high resonant frequency within a desired range to enhance the stability of the optical pick-up head during reading and writing operations.
The objective lens holding apparatus of the invention is for supporting the objective lens of the optical system in an optical pick-up head. The apparatus includes an objective lens holder, a supporting arm anchor dock, an upper supporting portion and a bottom supporting portion. The objective lens holder is used to support the objective lens. The supporting arm anchor dock is elastic and remains stationary relative to the optical axis of the objective lens. The upper supporting portion and the bottom supporting portion correspond to each other and are elastic. One end of the supporting portions connects to the objective lens holder and the other end connects to the supporting arm anchor dock. The two supporting portions may be extended to cross with each other at a location beyond the supporting arm anchor dock.
As the non-parallel and elastic supporting portions form an inclined angle with the supporting arm anchor dock in opposite directions, during the reading operation on the optical disk the inclined angles offset each other. As a result, the objective lens is prevented from incurring an inclined angle during yawing when the optical pick-up head reads the optical disk. Moreover, the elastic supporting arm anchor dock can dampen the high resonant frequency to enhance the stability of the optical pick-up head during read/write operations.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.